U.S. patent application number 12/685452 was filed with the patent office on 2010-05-06 for feedback-controlled body-bias voltage source.
Invention is credited to Tien-Min Chen.
Application Number | 20100109758 12/685452 |
Document ID | / |
Family ID | 41509906 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100109758 |
Kind Code |
A1 |
Chen; Tien-Min |
May 6, 2010 |
FEEDBACK-CONTROLLED BODY-BIAS VOLTAGE SOURCE
Abstract
A body-bias voltage source having an output monitor, charge
pump, and shunt. a shunt circuit having on/off control is coupled
to the output monitor and to the output of the charge pump. Upon
sensing that the output voltage of the charge pump is above a
desired value, the output monitor may disable the charge pump
circuit and may enable the shunt circuit to reduce the voltage at
the output of the charge pump. When the voltage output of the
charge pump is below the desired value, the output monitor may
disable the shunt circuit and may enable the charge pump circuit. A
shunt circuit having proportional control may be substituted for
the shunt circuit with on/off control.
Inventors: |
Chen; Tien-Min; (San Jose,
CA) |
Correspondence
Address: |
IV (TRANSMETA);C/O MURABITO, HAO & BARNES LLP
TWO NORTH MARKET STREET, THIRD FLOOR
SAN JOSE
CA
95113
US
|
Family ID: |
41509906 |
Appl. No.: |
12/685452 |
Filed: |
January 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10747016 |
Dec 23, 2003 |
7649402 |
|
|
12685452 |
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Current U.S.
Class: |
327/536 ;
327/535 |
Current CPC
Class: |
H02M 3/07 20130101; H02M
2003/078 20130101; G05F 1/46 20130101 |
Class at
Publication: |
327/536 ;
327/535 |
International
Class: |
G05F 1/10 20060101
G05F001/10 |
Claims
1-20. (canceled)
21. A system comprising: first circuitry operable for generating an
output voltage; second circuitry coupled to said first circuitry
and operable for adjusting said output voltage responsive to a
control signal; and an output monitor coupled to said first
circuitry and operable for comparing said output voltage and a
reference voltage and operable for generating said control signal
based on a result of said comparing, wherein said control signal
has a state that is proportional to a difference between said
output voltage and said reference voltage.
22. The system of claim 21 wherein said first circuitry comprises a
charge pump.
23. The system of claim 21 wherein said second circuitry comprises
a shunt circuit.
24. The system of claim 21 wherein an effective resistance of said
second circuitry is changed in proportion to said control
signal.
25. The system of claim 21 wherein said output monitor is operable
for enabling said second circuitry to provide a discharge path for
said output voltage in response to sensing an overvoltage
condition.
26. The system of claim 21 wherein said output monitor is operable
for enabling said first circuitry in response to sensing an
undervoltage condition.
27. The system of claim 21 wherein said output monitor is operable
for disabling said second circuitry in response to sensing an
undervoltage condition.
28. The system of claim 21 wherein said output monitor is operable
for cycling said second circuitry between enabled and disabled
states in response to sensing an undervoltage condition when said
first circuitry is enabled, wherein said second circuitry, when
enabled, provides a discharge path for said output voltage.
29. The system of claim 21 wherein said first circuitry is coupled
to a P-type well, and wherein said output voltage comprises a
negative voltage usable as a body bias voltage to bias said P-type
well.
30. The system of claim 21 wherein said first circuitry is coupled
to an N-type well, and wherein said output voltage comprises a
positive voltage usable as a body bias voltage to bias said N-type
well.
31. The system of claim 21 further comprising a current source and
a variable resistor coupled to said output monitor and operable for
providing said reference voltage.
32. The system of claim 21 wherein said output monitor comprises a
comparator.
33. A device comprising: a well disposed in a substrate; first
circuitry operable for generating a body bias voltage for biasing
said well; an output monitor coupled to said first circuitry and
operable for comparing said body bias voltage and a reference
voltage and for generating a control signal based on a result of
said comparing, wherein said control signal is proportional to a
difference between said output voltage and said reference voltage;
and second circuitry coupled to said first circuitry and operable
for adjusting said body bias voltage responsive to said control
signal.
34. The device of claim 33 wherein said first circuitry comprises a
charge pump and said second circuitry comprises a shunt
circuit.
35. The device of claim 33 wherein said output monitor is operable
for enabling said second circuitry to provide a discharge path for
said body bias voltage in response to sensing an overvoltage
condition.
36. The device of claim 33 wherein said output monitor is operable
for enabling said first circuitry in response to sensing an
undervoltage condition.
37. The device of claim 36 wherein said output monitor is operable
for disabling said second circuitry in response to sensing said
undervoltage condition.
38. The device of claim 33 wherein said output monitor is operable
for disabling said second circuitry in response to sensing an
undervoltage condition.
39. The device of claim 33 wherein said output monitor is operable
for cycling said second circuitry between an enabled state and a
disabled state in response to sensing an undervoltage condition
when said first circuitry is enabled, wherein said second circuitry
when enabled provides a discharge path for said body bias
voltage.
40. A method comprising: sensing a first voltage at an output
monitor coupled to an integrated circuit; sensing a reference
second voltage at said output monitor; generating a control signal
based on a comparison of said first voltage and said second
voltage, wherein said control signal has a state that is
proportional to a difference between said first voltage and said
second voltage; and adjusting said first voltage in response to
said control signal.
41. The method of claim 40 further comprising: enabling a discharge
path for said first voltage in response to sensing an overvoltage
condition; and varying an effective resistance of said discharge
path according to said control signal.
42. The method of claim 40 further comprising enabling a source of
said first voltage in response to sensing an undervoltage
condition.
43. The method of claim 40 further comprising disabling a discharge
path for said first voltage in response to sensing an undervoltage
condition.
44. The method of claim 40 further comprising cycling a discharge
path for said first voltage between an enabled state and a disabled
state in response to sensing an undervoltage condition when a
source of said first voltage is enabled, wherein in said enabled
state an effective resistance of said discharge path is varied
according to said control signal.
45. The method of claim 40 wherein said first voltage comprises a
negative voltage usable as a body bias voltage to bias a P-type
well of said integrated circuit.
46. The method of claim 40 wherein said first voltage comprises a
positive voltage usable as a body bias voltage to bias an N-type
well of said integrated circuit.
Description
RELATED UNITED STATES PATENT APPLICATIONS
[0001] This Application is a Continuation Application of the
co-pending, commonly-owned U.S. patent application with Ser. No.
10/747,016, filed Dec. 23, 2003, by Tien-Min Chen, and entitled
"Feedback-Controlled Body-Bias Voltage Source," which is hereby
incorporated by reference in its entirety.
[0002] This Application is related to U.S. patent application, Ser.
No. 10/747,015, now U.S. Pat. No. 7,129,771, by Tien-Min Chen,
filed on Dec. 23, 2003, entitled "Servo Loop for Well Bias Voltage
Source," and assigned to the assignee of the present invention.
[0003] This Application is related to U.S. patent application, Ser.
No. 10/746,539, by Tien-Min Chen and Robert Fu, filed on Dec. 23,
2003, entitled "A Precise Control Component for a Substrate
Potential Regulation Circuit," and assigned to the assignee of the
present invention.
[0004] This Application is related to U.S. patent application, Ser.
No. 10/747,022, now U.S. Pat. No. 7,012,461, by Tien-Min Chen,
filed on Dec. 23, 2003, entitled "A Charge Stabilizing Component
for a Substrate Potential Regulation Circuit," and assigned to the
assignee of the present invention.
FIELD OF THE INVENTION
[0005] Embodiments of the present invention relate to circuits for
providing operational voltages in complementary metal-oxide
semiconductor (CMOS) circuits. In particular, embodiments of the
present invention relate to circuits for providing a body-bias
voltage for CMOS transistors.
BACKGROUND ART
[0006] As the operating voltages for CMOS transistor circuits have
decreased, variations in the threshold voltages for the transistors
have become more significant. Although low operating voltages offer
the potential for reduced power consumption, threshold voltage
variations due to process and environmental variables often prevent
optimum efficiency and performance from being achieved due to
increased leakage currents.
[0007] Prior Art FIG. 1A shows a conventional CMOS inverter 100. A
P-type substrate 105 supports an NFET 110 and a PFET 120. The NFET
110 comprises a gate 112, source 113, and drain 114. The PFET 120
resides in an n-well 115, and comprises a gate 122, drain 123, and
a source 124. The substrate 105 and source 113 are coupled by a tie
130 that is connected to ground (GND), while source 124 and N-well
115 are coupled by a tie 135 that is connected to a supply voltage
(V.sub.DD). The input to the inverter is applied to the gates 112
and 122, with the output taken from the drain contact 125. In this
conventional configuration, the transistors are often treated as
three terminal devices.
[0008] Threshold voltage variations may be compensated for by
body-biasing. Body-biasing introduces a reverse bias potential
between the bulk and the source of the transistor that allows the
threshold voltage of the transistor to be adjusted electrically.
The purpose of body-biasing is to compensate for 1) process
variations; 2) temperature variations; 3) supply voltage
variations; 4) changes in frequency of operation; and 5) changing
levels of switching activity.
[0009] Prior Art FIG. 1B shows an inverter having connections for
body-biasing. Body-bias can provided to the PFET 120 through a
direct bias contact 150a, or by a buried n-well 140 using contact
150b. Similarly, body-bias may be provided to the NFET 110 by a
surface contact 155a, or by a backside contact 155b. An aperture
145 may be provided in the buried n-well 125 so that the bias
potential reaches the NFET 110. In general, a PFET 120 or an NFET
110 may be biased by one of the alternative contacts shown.
[0010] Depending upon the environmental and operational conditions,
a CMOS circuit may require different levels of bias for the
transistors. For example, a microprocessor that is executing a
computationally intensive routine for a real-time application will
typically be biased for maximum speed, whereas during periods of
low activity the bias will be adjusted to minimize leakage
current.
[0011] For a CMOS integrated circuit, the load presented to a
circuit providing a body-bias voltage and the bias circuit itself
may vary with the environmental and operational conditions of
integrated circuit. Thus, the variations in the required body-bias
voltage and the load to which it is applied should be taken into
account to achieve optimum performance.
SUMMARY OF INVENTION
[0012] Thus, a need exists for a system for providing a body-bias
voltage for CMOS transistors that is capable of adapting to varying
output voltage requirements and load conditions.
[0013] Accordingly, embodiments of the present invention provide a
system that uses feedback controlled charge pump to establishing a
desired output voltage. The system accepts an input reference
voltage that is related to the desired output voltage in order to
provide the desired output voltage.
[0014] In an embodiment of the present invention, a charge pump
having a voltage output and an enable input for on/off control is
coupled to an output monitor (e.g., a sense amplifier). The output
monitor is coupled to the output of the charge pump and to the
enable input of the charge pump. A shunt circuit having on/off
control is coupled to the output monitor and to the output of the
charge pump. Upon sensing that the output voltage of the charge
pump is above a desired value, the output monitor may disable the
charge pump circuit and may enable the shunt circuit to reduce the
voltage at the output of the charge pump. When the voltage output
of the charge pump is below the desired value, the output monitor
may disable the shunt circuit and may enable the charge pump
circuit.
[0015] In another embodiment similar to that described above, a
shunt circuit having proportional control is substituted for the
shunt circuit with on/off control. Upon sensing a deviation from a
desired output value at the output of the charge pump, the output
monitor provides a signal to the shunt circuit that is proportional
to the deviation at the charge pump output. The effective
resistance of the shunt is proportionally reduced in response to a
positive deviation and proportionally increased in response to a
negative deviation. Proportional control of the shunt circuit may
be combined with on/off control of the charge pump circuit to
regulate the output voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated in and
form a part of this specification, illustrate embodiments of the
invention and, together with the description, serve to explain the
principles of the invention:
[0017] Prior Art FIG. 1A shows a conventional CMOS inverter without
body-bias connections.
[0018] Prior Art FIG. 1B shows a conventional CMOS inverter with
body-bias connections.
[0019] FIG. 2 shows a block diagram of a feedback controlled
body-bias circuit in accordance with an embodiment of the present
claimed invention.
[0020] FIG. 3 shows a circuit diagram of a body-bias supply with a
servo loop for NFETs in accordance with an embodiment of the
present claimed invention.
[0021] FIG. 4 shows a circuit diagram of a body-bias supply with a
servo loop for PFETs in accordance with an embodiment of the
present claimed invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] In the following detailed description of the present
invention, a feedback-controlled body-bias circuit, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. However, it will be obvious
to one skilled in the art that the present invention may be
practiced without these specific details. In other instances well
known methods, procedures, components, and circuit elements have
not been described in detail as not to unnecessarily obscure
aspects of the present invention.
[0023] FIG. 2 shows a block diagram 200 of an embodiment of the
present invention. A charge pump 210 has an output coupled to
C.sub.load that represents a substrate or well. Since body-bias is
typically applied as a reverse bias to a p-n junction within a CMOS
device, the load seen by the body-bias voltage source is generally
a capacitive load; however, there is a certain amount of leakage
current, represented by R.sub.leak.
[0024] An output monitor 205 has a sense input coupled to the
output of the charge pump 210. The output of the charge pump is
compared to a reference voltage V.sub.ref by the output monitor
205. Upon sensing a positive or negative deviation (overvoltage or
undervoltage) that exceeds an allowed value, the output monitor
provides a control signal to the charge pump circuit 210 and/or a
shunt circuit 215.
[0025] For an overvoltage condition with loads having a large
C.sub.load and large R.sub.leak (small leakage current), simply
turning off the charge pump may not result in a sufficiently fast
discharge of C.sub.load to the desired value. Accordingly, the
shunt 215 may be enabled to provide a discharge path that allows
faster correction of the output voltage V.sub.out.
[0026] Upon sensing an undervoltage condition, the output monitor
205 may enable the charge pump circuit 210 and/or disable the shunt
circuit 215. In one embodiment, the charge pump is run
continuously, with the shunt being cycled between enabled and
disabled states to maintain the output voltage.
[0027] In determining the voltage deviation that is permitted in
the system, a deadband having upper and lower control points may be
used, or a single setpoint may be used (no allowable
deviation).
[0028] In an alternative embodiment, the output monitor 205
provides a proportional signal to the shunt circuit 215 that is
proportional instead of the on/off control described above. The
effective resistance of the shunt is proportionally reduced in
response to a positive deviation and proportionally increased in
response to a negative deviation. Proportional control is
preferably implemented using analog circuits, and thus is suitable
for use in a mixed-signal integrated circuit.
[0029] FIG. 3 shows a circuit diagram 300 of a body-bias supply
with a servo loop for NFETs in accordance with an embodiment of the
present claimed invention. The current source 305 and variable
resistor R combine to provide a reference voltage (e.g., V.sub.ref
of FIG. 2). The comparator 310, shunt 320, and charge pump 315
correspond to the output monitor 205, shunt 215, and charge pump
210 of FIG. 2. The output of charge pump 315 is a negative voltage
that may be used to bias a P-type substrate or well to provide a
body-bias for NFETs.
[0030] FIG. 4 shows a circuit diagram 400 of a body-bias supply
with a servo loop for PFETs in accordance with an embodiment of the
present claimed invention. The current sink 405 and variable
resistor R combine to provide a reference voltage (e.g., V.sub.ref
of FIG. 2). The comparator 410, shunt 420, and charge pump 415
correspond to the output monitor 205, shunt 215, and charge pump
210 of FIG. 2. The output of charge pump 315 is a positive voltage
that may be used to bias an N-type substrate or well to provide a
body-bias for PFETs.
[0031] A description of the circuits shown in FIG. 3 and FIG. 4 is
provided in the previously incorporated copending patent
application entitled "Servo Loop for Well Bias Voltage Source"
(U.S. Pat. No. 7,129,771). More specifically, descriptions of the
variable resistor R and shunt (320, 420) shown in FIG. 3 and FIG. 4
are provided in the previously incorporated copending patent
applications entitled "A Precise Control Component for a Substrate
Potential Regulation Circuit" and "A Charge Stabilizing Component
for a Substrate Potential Regulation Circuit" (U.S. Pat. No.
7,012,461).
[0032] The foregoing descriptions of specific embodiments of the
present invention have been presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms disclosed, and obviously many
modifications and variations are possible in light of the above
teaching. For example, an integrated circuit having a P-type
substrate and an N-well disposed therein is described. More
generally, the invention may be used with a semiconductor substrate
of either N-type or P-type having a complementary well disposed
therein. The embodiments were chosen and described in order to best
explain the principles of the invention and its practical
application, to thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications are suited to the particular use contemplated. It is
intended that the scope of the invention be defined by the claims
appended hereto and their equivalents.
* * * * *